IMPLANTABLE CARDIOVERTER DEFIBRILLATOR
Category: Cardiology Heart Health
Abstract : Implantable cardioverter defibrillator Definition The implantable cardioverter-defibrillator (ICD) is a surgically implanted electronic device that directs an electric charge directly into the heart to treat life-threatening arrhythmias. Purpose The implantable cardioverter-defibrillator is used to detect and stop life-threatening arrhythmias and restore a productive heartbeat
Implantable cardioverter defibrillator
Definition
The implantable cardioverter-defibrillator (ICD) is a surgically implanted electronic device that directs an electric charge directly into the heart to treat life-threatening arrhythmias.
Purpose
The implantable cardioverter-defibrillator is used to detect and stop life-threatening arrhythmias and restore a productive heartbeat that is able to provide adequate cardiac output to sustain life. The exact indications for the implantation of the device are controversial, but patients suffering from ventricular fibrillation (unproductive heartbeat), ventricular tachycardia (abnormally fast heartbeat), long QT syndrome (an inherited heart disease), or others at risk for sudden cardiac death are potential candidates for this device.
A study by the National Institute for Heart, Lung, and Blood of the National Institutes of Health showed a significant increase in survival for patients suffering from ventricular arrhythmias when ICD implant is compared to medication. Several follow-up studies indicate that this may be due to the marked increase in survival for the sickest patients, generally defined as those having a heart weakened to less than 50% of normal, as measured by the ability of the left side of the heart to pump blood. Overall, studies have documented a very low mortality rate of 1–2% annually for persons implanted with the device, compared to approximately 15–25% for patients on drug therapy.
Demographics
ICD implant is limited to patients that face the risk of sudden cardiac death from sustained ventricular arrhythmia, including ventricular tachycardia and ventricular fibrillation. Less than 1% of the more than 100,000 device implants done in the United States are performed on pediatric patients. Reduction in the risk of sudden cardiac death improves to less than 2% for both populations.
Diagnosis
Patients experiencing syncope (fainting) will be monitored with a cardiac monitor for arrhythmias. Following unsuccessful medical treatment for sustained ventricular arrhythmias, ICD implant will be indicated.
Description
Similar in structure to a pacemaker, an ICD has three main components: a generator, leads, and an electrode. The generator is encased in a small rectangular container, usually about 2 in (5 cm) wide and around 3 oz (85 g) in weight. Even smaller generators have been developed, measuring 1 in (2.5 cm) in diameter and weighing about 0.5 oz (14 g). The generator is powered by lithium batteries and is responsible for generating the electric shock. The generator is controlled by a computer chip that can be programmed to follow specific steps according to the input gathered from the heart.
The programming is initially set and can be changed using a wand programmer, a device that communicates by radio waves through the chest of the patient after implantation. One or two leads, or wires, are attached to the generator. These wires are generally made of platinum with an insulating coating of either silicone or polyurethane. The leads carry the electric shock from the generator. At the tip of each lead is a tiny device called an electrode that delivers the necessary electrical shock to the heart. Thus, the electric shock is created by the generator, carried by the leads, and delivered by the electrodes to the heart. The decision of where to put the leads depends on the needs of the patient, but they can be located in the left ventricle, the left atrium, or both.
According to the American College of Cardiology, more than 100,000 persons worldwide currently have an ICD. The battery-powered device rescues the patient from a life-threatening arrhythmia by performing a number of functions in order to reestablish normal heart rhythm, which varies with the particular problem of the patient. Specifically, if encountered with ventricular tachycardia, many devices will begin treatment with a pacing regimen. If the tachycardia is not too fast, the ICD can deliver several pacing signals in a row. When those signals stop, the heart may go back to a normal rhythm. If the pacing treatment is not successful, many devices will move onto cardioversion. With cardioversion, a mild shock is sent to the heart to stop the fast heartbeat.
If the problem detected is ventricular fibrillation, a stronger shock called a defibrillation is sent. This stronger shock can stop the fast rhythm and help the heartbeat return to normal. Finally, many ICDs can also detect heartbeats that are too slow; they can act like a pacemaker and bring the heart rate up to normal. ICDs that defibrillate both the ventricles and the atria have also been developed. Such devices not only provide dualchamber pacing but also can distinguish ventricular from atrial fibrillation. Patients that experience both atrial and ventricle fibrillations, or atrial fibrillation alone, that would not be controlled with a single-chamber device are candidates for this kind of ICD.
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